The E ciency Comparison of Taxes under Monopolistic Competition with Heterogenous Firms and Variable Markups November 9, 23 Abstract This paper compares the e ciency implications of aggregate output equivalent unit versus advalorem tax regimes when monopolistically competitive rms produce di erentiated products with either homogenous or heterogenous costs. The model allows for rms to price at a variable markup over marginal cost. In line with most prior ndings the superiority of ad-valorem tax continues to hold when rms have homogenous costs. However, I nd that a unit tax becomes more e cient when rms have heterogenous costs and unit tax is relatively high. The model generates both the selection of rms and reallocation of resources, in addition to the well-documented e ects of tax regimes on rms output and pricing decisions. Furthermore, these two tax regimes have di erential e ects on mark-up distributions: an ad-valorem tax distorts the mark-up distribution of rms in favor of more productive rms. The aggregate productivity is therefore higher compared to an output equivalent unit tax. A more productive market with lower prices ampli es the superiority of the ad-valorem tax at lower revenue requirements. However, I nd that when the unit tax is relatively high, the excessive exit rate under an ad-valorem tax regime overturns the welfare superiority argument in favor of a unit tax regime. JEL Classi cations: L H2 H25 Key Words: Unit Tax, Ad-valorem Tax, E ciency, Monopolistic Competition, Heterogenous Firms Introduction Governments use unit or ad-valorem tax regimes not only as a form of revenue extraction, they also aim to target a consumption/production level in an industry. They have environmental or health concerns or they use import quotas to protect domestic industries from foreign competition. These taxes are usually refered to as corrective taxes. The relative e ciency of two di erent ways of implementing taxation for perfectly competitive markets, monopolies and oligopolies, has been extensively discussed. Little attention has been devoted to monopolistically competitive markets. Furthermore, there is a large empirical literature documenting rm heterogeneity even in narrowly de ned industries 2. Meanwhile, empirical evidence supports that there is an adjustment in mark-ups when rms face competitive pressure 3. Therefore, analyzing the relative e ciency of unit and ad-valorem corrective tax regimes in a monopolistically competitive market with heterogenous rms and endogenous markups lls an important gap in the public economics literature. In this paper I rst show that in a model of monopolistic competition where homogenous cost rms produce di erentiated products and consumer preferences are described such that rms can endogenously adjust their markups, an ad-valorem tax welfare dominates an output equivalent unit tax with redistributed tax revenue to consumers. The result is driven solely by the typical trade-o between revenue Except Schröder (24), and Schröder and Sørensen (2), Dröge and Schröder (28) 2 See Bartelsman and Doms (2) for a survey of empirical evidence on rm level heterogeneity in productivity. 3 See, De Loecker et al (22).for recent discussions on how a trade liberalization a ects the mark-up distribution of rms over marginal costs.
extraction and variety generation. On one hand, under an ad-valorem tax regime rms tend to decrease their price and increase their output. An ad-valorem tax is therefore a better revenue extractor. On the other hand, a unit tax generates greater variety due to the larger tax overshift, enabling rms to survive at lower output levels. This result contradicts with the ndings of Dröge and Schröder (29). They compare the welfare e ects of unit and ad-valorem taxes in a Dixit-Stiglitz type monopolistic competition model using equal output criterion. They argue that unit tax by generating many small rms welfare dominates the ad-valorem tax. Yet, the same model with equal yield comparison con rms the superiority of ad-valorem tax in Schröder (24). Next, when one allows for heterogenous cost the superiority of an ad-valorem tax is challenged. A unit tax becomes welfare-superior when the government tax requirement is relatively high. The reasons for the inverse ranking are two-fold. Firstly, rm heterogeneity in costs increases both the gap in prices and number of rms between the two tax regimes. Secondly, variable markup pricing ampli es this gap even further. I can only observe these e ects under heterogenous cost and variable markup assumptions since the two tax regimes a ect rms markup distribution and thus prices di erently. More speci cally, the ad-valorem tax distorts the relative cost advantage of rms in favor of more productive rms. The selection and reallocation e ects among heterogeneous rms therefore allow only relatively more productive rms to survive in the market. Aggregate productivity is therefore higher compared to an output equivalent unit tax. This has two opposing e ects on welfare. On the one hand, higher aggregate productivity results in even lower prices by amplifying the lower price advantage of ad-valorem taxes. On the other hand, higher aggregate productivity decreases total variety further since rms can only survive by operating as larger rms. At higher tax levels, the welfare loss from lesser variety overturns the superiority of ad-valorem tax in favor of the unit tax. Contrary to the focus of this paper, generated tax revenue is the focus of the majority of the publics economics literature. The early contributions state that in a perfectly competitive market whether tax is ad-valorem or unit does not matter; since rms are price takers, only the cost-price increase generated by the tax is relevant. Consequently, for every unit tax rate there exists an equivalent ad-valorem tax level. On the other extreme, when there is a monopoly this equivalence result breaks down: an advalorem tax generates more welfare than a unit tax (see Suits and Musgrave (953), and Skeath and Trendel (994)). The result is driven by the fact that a pro t-maximizing monopolist increases its output when an ad-valorem tax is imposed. Higher output reduces prices, decreasing the wedge between the price consumers pay and the price producers receive. Consumers are therefore better o with greater output and lower prices compared to a unit tax. The superiority of ad-valorem tax continues to hold for a wide range of market structures. 4 The recent contribution to the equal yield tax criterion literature can be discussed in two dimensions: cost asymmetries and short run versus long run analysis. A unit tax allows rms to survive at lower output levels. Thus more rms/varieties can survive compared to an ad-valorem tax. Since the number of rms is xed in the short run, the variety e ect that usually favors unit taxation is shut down. The ability of ad-valorem taxes to create lower prices still holds. As a result, analysis with homogenous costs in the short run supports ad-valorem taxation (Delipalla and Keen (992), and Anderson et al. (2)). In the long run both the variety e ect and the price e ect are present. Schröder (24) choose a Dixit-Stiglitz utility in order to model consumers love of variety in a monopolistic competition setting. He shows that an equal yield ad-valorem tax remains welfare superior under monopolistic competition settings. Adding cost asymmetries to Schröder s (24) model does not change the results for monopolistic competition models (Schröder and Sørensen (2)). There is a recent discussion in international trade literature that recalculates gains from trade with variable mark-ups (Arkolakis et al. (22) and Edmond et al. (22)). They mainly argue that markups are incresing with rm level productivity. With trade liberalization, through the exit of low productivity rms, consumer expenditures are transefered towards more productive rms. The prices of those higher productive rms are lower. On the other hand, the price cost margins are higher. Thus, when we aggregate the markups with market shares, the aggregate markups may increase due to trade liberalization. In this 4 See Keen (998) for a review of the literature. 2
paper, the tax regimes distorts the market such that unit taxes have no e ect on the markup distribution since the rms can fully pass the burden onto consumers. On the other hand, under an output equivalent ad-valorem tax regime rms charge lower markups. This further decreases prices compared to unit taxes. As a result, under an ad valorem tax the market becomes more competitive, resulting in even lower prices but fewer varieties. The model used in this paper is based on Melitz and Ottaviano (28) which gives closed form solutions. This allows the policy maker to acquire comparative statistics with respect to market size, dispersion of marginal costs, and the level of love for variety. We also learn that tax regimes are not simply revenue extraction or output corrective instruments for governments but are also exogenous mechanisms that a ect the market structure and aggregate productivity within an industry. If the government prefers to support productive rms and eliminate relatively less productive ones, then an ad-valorem tax is the appropriate tax regime. 2 Model The model used in this paper is based on Melitz and Ottaviano (28) 5 There are L identical consumers of size. Their preferences are de ned over a continuum of di erentiated products and a homogenous good. They choose di erentiated products from the set of varieties, : A homogenous good is indexed by ; and a di erentiated good is indexed by i. A consumer utility function is then: U = q + i2 q i di 2 i2 (q i ) 2 di 2 @ i2 q i dia 2 ; () where q is the homogenous good consumption and q i is the di erentiated good consumption of variety i. ; ; and are the positive demand parameters. The degree of product di erentiation increases with and consumers love for variety is re ected in R i2 (q i) 2 di. The demand for the homogenous good is assumed to be positive, and its price is normalized to one. From utility maximization, a consumer s inverse demand for each di erentiated variety is then given as: where Q = i2 q i di is the total quantity consumed. market demand for variety i which is given as: p i = q i Q; (2) When I aggregate over all consumers, the linear q i = + N p i + N P + N e ; where N is the mass of di erentiated varieties, and P e = N p i di is the average price over all prices. In this economy the technology to produce the homogenous good is identical across rms. It is produced under constant returns to scale at a cost of one unit of labor. Consumers in this economy are endowed with one unit of labor. Labor is inelastically supplied, and there is no leisure in the utility function. Furthermore, labor is the only factor of production. The demand for the homogenous good is ensured to be positive with the assumption that income is high enough and the homogenous good is freely traded in a perfectly competitive market. If the price of the homogenous good is normalized to one and since workers receive their revenue of marginal product, the wage is unity. 5 See Melitz and Ottaviano (28) for a detailed description of the model. i2 3
The model features of consumers and homogenous good producers are identical under both homogenous and heterogenous cost cases. Going forward, I lay out the remaining features of the model that di er for di erentiated good producers when they have either homogenous or heterogenous costs, and when they face either ad-valorem or unit tax regimes. 3 Relative E ciency of Unit and Ad-valorem Taxes with Symmetric Costs Firms produce di erentiated goods at a constant marginal cost of c: 6 These rms must pay a sunk entry cost of f e in order to enter the market. 7 There is free entry and exit. Firms therefore enter the market if the expected pro t of a rm covers the sunk entry cost. This condition determines the total mass of rms and variety in the market, and is called the free entry condition. Ad-Valorem Tax Regime: I rst analyze the market if the government collects ad-valorem taxes as the fraction t of the price per unit of a good sold in the market. In this economy a pro t-maximizing rm chooses an optimal amount of output given the inverse demand it faces. A rm supplies q t (c) units given as: q t (c) = c p t (c) : (3) t where going forward subscript t refers to ad-valorem taxing economy parameters. There is no uncertainty regarding the technology of a rm in di erentiated markets. A potential entrant will enter the market if the pro t covers the sunk entry cost. The free entry condition of rms is therefore given as: t (c) f e = : The equilibrium in the market is characterized by the pro t maximizing price, output by each rm, and total varieties in the market given as: s f e q t (c) = ( t) ; s f e p t (c) = ( t) + c t ; and N t = Q t q t (c) = q c t 2 fe ( t) q fe ( t) : Unit Tax Regime: Similarly, the market equilibrium is de ned if the government collects s for every unit sold in the market. As a result the rms s pro t maximizing output becomes: q s (c) = (p s(c) (c + s)) : where going forward subscript s refers to unit taxing economy parameters. The free entry condition is characterized similarly to that of an ad-valorem tax as s (c) f e = : The equilibrium values of pro t 6 There is no need to add a xed cost of production in order to generate a nite mass of rms in the market. The linear demand caps the maximum price a rm can charge in order to make positive pro t. 7 Since wage is unity, all cost gures mentioned in this paper are in unit labor requirements. 4
maximizing the price, quantity, and equilibrium number of varieties are given as: s f e q s (c) = ; p s (c) = p f e + c + s; and N s = Q s q s (c) = c s 2 p fe : q fe The welfare is calculated as the sum of consumer surplus and tax revenue and producer surplus in this economy. The producer surplus is zero since there is free entry and exit. Since tax revenue is redistributed back to consumers, the calculated welfare per person is identical to the utility (expression ()) derived from consuming all the varieties in the market. Therefore, the welfare rankings for the two tax regimes are also valid for utility of consumers. Proposition The equilibrium values of output per rm, pro t maximizing price, variety, and tax revenue for an ad valorem and a unit tax under output equivalence are compared as:. An ad-valorem tax regime creates larger rms, i.e. q s < q t. 2. Firms under an ad-valorem tax regime price lower, i.e. p s > p t : 3. An ad-valorem tax creates less variety, i.e. N s > N t ; 4. The tax revenue and consumer surplus created by the ad-valorem tax regime is greater compared to that of an output equivalent unit tax regime. 5. Welfare if de ned as the sum of tax revenue and consumer surplus is superior under an ad-valorem tax regime compared to that under an output equivalent unit tax regime. Proof. Provided in the appendix. Proposition one states that when rms homogenous in costs compete in a monopolistically competitive markets and consumers have a linear demand for di erentiated products, then an ad-valorem tax is a welfare superior method of corrective tax. This result contradicts the previous ndings of welfare rankings with homogenous rms in monopolistically competitive markets by Dröge and Schröder (29) but con rms the results of Schröder(28) when equal yield criterion is used. In both papers, consumer preferences are characterized by constant elasticities of demand. This result further strengthens the superiority of ad-valorem taxes under Cournot competition with free entry and exit (Anderson et al. (2). However, it contradicts the inverse welfare ranking of Anderson et al. (2) for the case of Bertrand competition and product di erentiation with a discrete choice framework of exponentially distributed match values. All of the above mentioned models have two common forces at work. First, an ad-valorem tax makes the demand curve more elastic. As a result, a pro t-maximizing rm produces more at a lower price. This decreases the wedge between the price consumers pay and the price producers receive. Consumers therefore bene t from lower prices compared to a unit tax. Second, a unit tax acts like an increase in marginal cost. Firms therefore tend to decrease their output while they increase their prices. A higher operating surplus and smaller outputs are therefore su cient to o set the xed entry cost of entering the market. This allows more rms to exist in the market under unit taxes. For ad-valorem taxes lower prices tend to increase welfare, while less variety decreases welfare if consumers have love for variety. The relative e ciency results are driven solely by the dominance of one over the other. In this model speci cation rms fully pass the unit tax on to consumers, while an ad-valorem tax is shared between both producers and consumers. As a result the price e ect dominates the variety e ect; an ad-valorem tax generates greater consumer surplus, tax revenue, and as a result welfare. 5
4 Relative E ciency of Unit and Ad-Valorem Taxes with Asymmetric Costs I now reconstruct a model of rms producing di erentiated products at heterogenous marginal cost of production,!: Potential entrants must pay a sunk entry cost f e in order to learn their marginal cost of production. Once the entrants pay the entry cost, they draw their marginal costs =! from a common Pareto distribution with support on [;!] and dispersion parameter k. This implies that marginal cost draws come from a cumulative distribution G(!) =! k! : The parameter k indexes the dispersion of cost draws. Once a rm is in the market pro t is maximized by taking the total number of varieties and average prices in the market as given. Since the entry cost f e is sunk, rms that are able to cover their marginal costs survive in the market and continue to produce. This implies that there exists a marginal rm making zero pro t. The marginal rm s marginal cost of production is labeled as! (zero cuto condition).! Finally, prior to entry, the expected pro t of a rm is (!)dg(!) f e : Firms will enter until this pro t is driven to zero giving us the free entry condition. Notice that both the zero cuto condition and the free entry condition can be written as functions of!, the number of rms and model parameters. Both the cuto marginal cost of production and the number of rms can therefore be uniquely identi ed. I further analyze the relative e ciency of ad-valorem and unit taxes for a monopolistically competitive market of rms selling di erentiated goods produced with heterogenous costs. I show that the heterogeneity of rms unseats the superiority of ad-valorem tax at higher levels of unit taxes. I previously discussed the general properties of the model for rms of heterogenous costs; I now detail the di erences caused by di erent regimes and heterogenous costs. Ad-valorem Tax Regime: If the government collects t percent of the price per unit of a good sold, then the pro t maximizing output of a rm with marginal cost of production! is: q t (!) = p t (!)! : (4) t Any potential entrant who pays the sunk entry cost and learns its marginal cost of production decides whether to stay in the market or exit immediately depending on the pro t it can make. A marginal rm therefore makes zero pro t. The expression below de nes! t as the marginal cost of production for the marginal rm:! t t = Q t: (5) The cuto marginal cost! t summarizes the e ects of both the average price and the number of rms on the price and output measures of all rms. All of these measures can be written as functions of only the rm s own marginal cost! and the marginal rm s! t as:! t The free entry condition is also rede ned as t (!)dg(!) q t (!) = (! t!) ; and (6) 2 t p t (!) = (! t +!) : 2 t f e : If the above measures are used and! t is solved for; I can then de ne the cut o marginal cost as a function of the model parameters:! t = f e (k + )(k + 2)2 (!) k k+2 ( t) : (7) 6
The total number of varieties N t is calculated using the zero-cuto condition and by calculating the total output Q t : Unit Tax Regime: I now de ne the marginal rm, output, and price measures for all rms under a unit tax policy where the government collects s for each unit sold. A rm s pro t maximizing output therefore becomes: q s (!) = (p s(!) (! + s)) : (8) If the cost of production of the marginal rm making zero pro t in this economy is labeled as! s; then equating the pro t of the marginal rm to zero gives us the zero cuto condition as:! s + s = Q s : (9) I can rewrite the output and price measures of all rms in terms of cuto marginal cost! s and marginal cost of the rms as: q s (!) = 2 (! s!); and () p s (!) = 2 (! s +!) + s: Furthermore, the free entry condition also de nes the marginal rm by equating the ex-ante expected pro ts to the sunk entry cost paid. I can de ne! s as:! s = f e (k + )(k + 2)2 (!) k k+2 : () Notice that the cuto marginal cost for the unit tax is independent of the tax rate. This is because a unit tax is fully passed on to consumers. Furthermore, all tax revenue collected by the government is redistributed back to consumers. The marginal rm is therefore not a ected by the unit tax regime. I have described the model and two di erent taxation methods. The aim of this paper is to compare the resulting di erences in the welfare, created number of varieties, and most importantly the relative e ciency of the industry as a whole. I provide this using the total output equivalence condition. Proposition 2 The equilibrium values of variety, tax revenue, consumer surplus, the cuto marginal cost of production for ad valorem and unit taxes are compared as:. The marginal rm has lower marginal cost of production under an ad-valorem tax regime, i.e.! s >! t : Thus the industry is more productive under ad-valorem tax regime. 2. The variety created under an ad-valorem tax is less than a unit tax, i.e. N t < N s : 3. The tax revenue created by the ad-valorem tax regime is less compared to that of a unit tax regime, T R s > T R t : 4. The consumer surplus from the ad-valorem tax regime is greater compared to that of a unit tax regime, CS s < CS t : 5. Welfare is de ned as the sum of consumer surplus and tax revenue and it is superior under a unit tax regime compared to that of an ad-valorem tax regime when unit taxes are higher. Proof. Provided in the appendix. I nd that when cost asymmetry is added to a model of rms competing monopolistically and consumers having quadratic utility functions a unit tax is welfare superior to an output equivalent ad-valorem 7
tax for higher values of unit taxes. This result challenges the parameter-independent superiority of advalorem taxes (unit taxes) with homogenous costs in this paper (Dröge and Schröder (29)). A unit tax unseats an ad-valorem tax in this model is not only due to the appreciation of higher variety generated by unit taxes. In the presence of cost asymmetries and variable markup pricing these tax instruments a ect the distribution of mark-ups, thus prices di erently. A unit tax is fully passed onto consumers, and the distribution of mark-ups is not a ected. However, an ad-valorem tax distorts the distribution of mark-ups in favor of more productive rms. Market production is therefore reallocated toward more productive rms. The productivity of the marginal rm that makes zero pro t becomes less than that under a unit tax. The selection and reallocation of recourses exacerbate the price e ciency of ad-valorem taxes while decreasing the number of varieties that can survive even further compared to unit taxes. In Schröder and Sørensen s (2) model where heterogenous rms compete in monopolistically competitive markets and consumer preferences are represented by CES utility functions, the only force that is present is the selection of rms and reallocation of resources. Because of the CES preferences (constant mark-up assumption), they can not generate the di erential e ects of tax regimes on markup distribution. Surprisingly, having only selection e ects is not enough to unseat the superiority of ad-valorem tax whereas having also the existence of variable markup pricing overturns this superiority in favor of the unit tax. When rms face an ad-valorem tax regime they pay part of the tax burden, and this burden increases as rms becomes less productive. Pro t-maximizing rms therefore decrease their mark-ups and increase their production in order to avoid paying this burden; this in return decreases the relative demand for their products. Thus, the productivity of the surviving marginal rm has to be even higher to o set the lower mark-up and residual demand. That is to say heterogeneity exacerbates the price and variety gap between the two tax regimes, and variable mark-up pricing widens this gap even further. Surprisingly, contrary to many of the welfare ranking analysis, this model generates a higher consumer surplus under the ad-valorem tax regime and a higher tax revenue under the unit tax regime. This inverse ranking is a result of the existence of rm heterogeneity and variable mark-up pricing. Under an advalorem tax regime both the prices and number of varieties are lower. An output equivalent unit tax therefore generates more revenue. On the other hand, lower prices are valued by consumers even when they also have preferences for variety. 5 Conclusion The e ect of market structure and cost asymmetries of equal yield unit and ad-valorem taxes on welfare of consumers has been extensively discussed. The importance of variable mark-ups when calculating welfare especially with heterogenous rms is the recent discussion in international trade. Thus, this paper studies the welfare implications of output equivalent unit and ad-valorem taxes in a model of monopolistic competition with heterogenous rms and a utility function that allows variable mark-ups. The discussion contributes mainly to the public economics and the environmental economics literature on corrective taxes where little has been done with heterogenous rms. Without cost asymmetries, an ad-valorem tax is superior. However when including cost asymmetries I observe that a unit tax dominates an ad-valorem tax for higher levels of unit taxes. This inverse ranking is a result of both heterogeneity and variable markup pricing. Both e ects increase the gap between the price and variety generated under these two tax regimes. Thus at higher levels of taxation, the market under an ad-valorem tax becomes so competitive that the greater variety generated by the unit tax is more appreciated by society since it also values variety. References [] Anderson, S.P., de Palma, A., and Kreider, B., 2. The e ciency of indirect taxes under imperfect competition. Journal of Public Economics. 8(2), 23 25. 8
[2] Arkolakis, C., Costinot, A., Donaldson, D., and Rodriguez-Clare, A. 22. The elusive procompetitive e ects of trade. mimeo [3] Bartelsman, E. J., Doms, M.E., 2 Understanding productivity: Lessons from longitudinal microdata Journal of Economic Literature. 3,569-594. [4] Delipalla, S., Keen, M., 992. The comparison between ad valorem and speci c taxation under imperfect competition. Journal of Public Economics. 49, 35-367. [5] De Loecker, J., Goldberg, P.K., Khandelwal, A. and Pavcnik, N. 22 Prices, Markups and Trade Reform," Princeton University working paper. [6] Dröge,S., Schröder, P.J.H., 29. The welfare comparison of corrective ad valorem and unit taxes under monopolistic competition. International Journal of Tax and Public Finance, 6, 64-75 [7] Edmond, C., Midrigan, V., Yu, D. X., 22 Competition, markups, and gains from international trade. mimeo [8] Keen, M., 998. The balance between speci c and ad-valorem taxation. Fiscal Studies. 9, -37. [9] Melitz M., Ottaviano,G., 28. Market size, trade, and productivity. Review of Economic Studies. 75, 295-36 [] Schröder,P.J.H., 24. The comparison between ad-valorem and unit taxes under monopolistic competition. Journal of Economics. 83, 28-292 [] Schröder, P.J.H., Sørensen, A., 2. Ad valorem versus unit taxes: Monopolistic competition, heterogeneous rms, and intra-industry reallocations, Journal of Economics. (3), 247-265. [2] Skeath, S. Trendel, A.G., 994. A Pareto comparison of ad valorem and unit taxes in noncompetitive environments. Journal of Public Economics. 53(), 53-7. [3] Suits, D. B., Musgrave, R.A., 953. Ad valorem and unit taxes compared. Quarterly Journal of Economics. 67, 598-64. APPENDIX Proof of Proposition (Symmetric Cost Case): I must rst answer the following question: what is the level of unit tax that creates the same level of output as the ad-valorem tax rate t: I therefore rearrange inverse demand functions (eq.(2)) for the two tax regimes. I nd that Q t = p t + q t, and similarly Q s = p s + q s : Since our comparison unit is equal total output, I can conclude that: p t + q t = p s + q s : (2) When I use the supply function (eq.(4) and eq.(8)) and equilibrium values for both regimes (eq.(6) and eq.()), I nd the output equivalent unit tax rate as a function of model parameters: s = tc t + 2p f e p (3) t Firms under a unit tax regime are smaller and prices are higher than those under an ad-valorem tax regime. The output per- rm comparison is straightforward from the equilibrium values, q t = q fe ( t) and q s = q fe. For any t 2 (; ); q s < q t : Furthermore, following eq.(2) I can conclude that p s > p t : 9
Similarly, the total output equivalence gives fewer total varieties under an ad-valorem tax compared to a unit tax regime; N s > N t : Tax revenue on the other hand is not straightforward. Since the total output level is equal, one can simply compare the tax revenue collected per unit of output. Under a unit tax this value is s; whereas under an ad-valorem tax regime the per unit tax revenue is tp t : From eq.(3), s = tc t + 2(q t q s ): Similarly, tp t = tq t + tc t : The di erence between the tax revenues per unit is therefore equal to: T R t T R s Q = tp t s; = (2q s (2 t)q t ) ; and > for all t 2 (; ): The consumer surplus under both regimes is the utility created by consuming both the numeraire good and di erentiated goods net of money spent on them. The consumer surplus values under both regimes can therefore be written as: CS t = q o + Q t 2 N t(q t ) 2 2 (Q t) 2 p t Q t p o q o ; and CS s = q o + Q s 2 N s(q s ) 2 2 (Q s) 2 p s Q s p o q o : The tax regimes are output equivalent and the price of the numeraire good is normalized to. If I use these two information and take the di erence between the two consumer surpluses, I nd CS s CS t = Q( 2 q t = Q( 2 q s 2 q s + q s q t ); and 2 q t): Using eq. (2), I can further simplify the above expression to: CS s CS t = Q( 2 q s 2 q t): Since q s < q t ; the di erence in consumer surpluses under two regimes is: CS s CS t < for all model parameters and t 2 (; ): Finally, welfare under an ad-valorem tax regime is higher compared to unit tax regime because it creates greater consumer surplus and tax revenue. Proof of Proposition 2 (Asymmetric Cost Case): I should rst compare the cuto marginal cost values under both regimes. Eq.(7) and () give the direct relationship between! s and! t as! t = ( t) k+2! s : Since t is between and ; I conclude that! t <! s: I use equal output criterion with redistributed tax revenue in order to show the relative ranking of the variety created. The output created by all the rms in the market under an ad-valorem tax is given as:! t Q t = q(w)dg(wjw <! t ); =! t 2 (! s! t = 2(k + ) t N t:!)dg(wjw <! t ); and
Similarly, the total output under a unit tax regime is Q s = 2(k+)! sn s ; and additionally! t t >! s: Furthermore, I de ned the equivalency of these two regimes through output; as a result N s > N t : A unit tax creates greater variety than the output equivalent ad-valorem tax. The total tax collected from a rm with a marginal cost of production! is tp t (w)q t (w): In order to calculate the total tax collected from all the rms I aggregated the per- rm collected tax over their respective marginal cost values given as:! t T R t = tp(w)q(w)dg(wjw <! t ); =! t = 2 t 4 (! t +!) t t k + 2 ( t) 2 (! t ) 2 N t : (! t!) dg(wjw <! t ); and t If I further simplify the expression using the total output Q t calculated above, I nd T R t = t k+2! t Q t : I can similarly aggregate the tax collected from a single rm with a marginal cost of production! in order to calculate the total tax revenue created under a unit tax. The per- rm tax revenue is sq s (w): If I aggregate the overall surviving rms in the market, I nd that T R s equals 2 k+ s! sn s ; or simply sq s : In order to compare the tax revenue collected under both regimes I take the di erence of tax revenues calculated above: t k + T R s T R t = sq s t k + 2! t Q t : Since the total output is equal under both regimes I use the total output, call it Q, as a common factor. Furthermore, by using the zero cut o conditions in eq.(5), (9), and the equivalency de nition, I nd the output equivalent tax rate s as a function of a given ad-valorem rate t as s =! t t! s: If I insert in the expression for s and common factor Q I nd:! T R s T R t = Q t! t k + s t t k + 2! t : If I insert the equality between the cuto rates driven from free entry condition! t = ( t) k+2! s back into the above expression, the expression becomes a function of t, k and common multipliers: T R s T R t = Q! s ( t) k+2 t t k + ( t) k+2 t k + 2 The expression above is a continuous function for t 2 (; ); and at t = the di erence is zero. Furthermore, lim t! (T R s T R t ) = : Finally, d(t Rs T Rt) dt = k+ ( t) (k+)=(k+2) t (k+2) 2 t > for all t values between and : This means that the di erence of tax revenues under a unit tax and an output equivalent ad-valorem tax is not only always positive but is also increasing for t 2 (; ): The consumer surplus under a tax regime is the utility driven by consuming the di erentiated products and the numeraire good minus the cost of consuming those goods. The consumer surplus under an advalorem tax is therefore:! t CS t = q + Q t 2 qt 2 (w)dg(wjw <! t )! t = q + Q t 2(k + 2) t Q t 2 (Q t) 2 p q! t! t 2 (Q t) 2 k + p q k + 2 t Q t:! : t k+ p t (!)q t (w)dg(wjw <! t ); and
Similarly, the consumer surplus under a unit tax is q +Q s 2(k+2)! sq s 2 (Q s) 2 k+ p q k+2! sq s sq s : If I calculate the di erence between the consumer surplus under a unit tax and an ad-valorem tax taking into account that the price of a numeraire good is one and total output levels are equal at Q I nd: CS s CS t = 2(k + 2)! sq k +! k + 2! t sq sq + 2(k + 2) t Q + k +! t Q; and k + 2 t k +! = Q 2(k + 2)! s k + 2! t s s + 2(k + 2) t + k +! t : k + 2 t I insert unit tax rate s as a function of the cuto marginal cost values s =! t t! s back into the above expression and nd: CS s CS t = Q 2(k + 2) <.! s! t ; and t Thus, the consumer surplus generated under an ad-valorem tax is always greater than the consumer surplus generated under a unit tax. Welfare is on the other hand does not have a clear ranking. Under a unit tax regime welfare is therefore: W s = CS s + T R s, = q + Q s 2(k + 2)! sq s 2 (Q s) 2 p q k + = Q s 2(k + 2)! s 2 Q s k + k + 2! s : k + 2! sq s sq s + sq s and Similarly, welfare under an ad-valorem tax is: W t = CS t + T R t! t = q + Q t 2(k + 2) t Q t 2 (Q t) 2 k +! t p q k + 2 t Q t + t k + t k + 2! t Q t and! t = Q 2(k + 2) t 2 Q k +! t t k + 2 t + t k + t k + 2! t : By taking the di erence between both regimes I nd: k +! W s W t = Q 2(k + 2)! s k + 2! t s + 2(k + 2) t + k +! t t k + k + 2 t t k + 2! t! = Q! s 3 k k + 2 2 + ( t) =(k+2) + (k + )( t) =(k+2) : 2 ( t) ; and The expression above is zero for t = and is continuous for t 2 (; ): Furthermore, lim t! (W s W t ) = : The derivative of the di erence function with respect to t is Q! s k+ ( t) (k+)=(k+2) 2t (k+2) 2 t : The derivative is positive for t > :5, and zero for t = :5. This implies that the di erence function begins at zero, and decreases up to t = :5. The di erence reaches its minimum at t = :5 and begins to increase until it reaches for t = : Thus, welfare under a unit tax regime is greater than an output equivalent ad-valorem tax regime if t is large. 2